JP 2005-88769 A discloses a travel safety device of a working machine, which is provided with a “deadman clutch lever” intended to reduce fatigue of a human operator operating the working machine and an emergent stop mechanism for stopping the working machine in case of an emergency during rearward travel. Further, JP 2006-116977 A discloses a travel clutch mechanism including a main clutch lever disposed above an operating handle and side clutch levers disposed beneath the operating handle.
The travel safe device disclosed in JP 2005-88769 A includes a release rod disposed to protrude rearwardly of the rear end of a handle post and movable in a front-rear direction, and a holding plate for holding the deadman clutch lever in an ON position. The holding plate holds the deadman clutch lever in the ON position even when a human operator releases the deadman clutch lever after first gripping and moving the deadman clutch lever into the ON position and then moving a compression lever rearwardly. In an emergency, the release rod is moved forward to release the holding plate and place a travel clutch in an OFF state. Thus, the working machine can keep traveling without the human operator continuing gripping the deadman clutch lever together with a grip portion of the operating handle during travel of the working machine.
However, with the aforementioned travel safety device, there would arise the problem that, when the travel clutch is to be held in the ON state, the human operator has to move the release rod rearwardly by putting his or her finger on the release rod after gripping the deadman clutch lever together with the grip portion of the operating handle, which would undesirably increase the number of necessary operation steps, take a lot of trouble and lower the operability.
With the travel clutch lever disclosed in JP 2006-116977 A, a toggle spring retained on the main clutch lever crosses upward over the pivot shaft (or pivot point) of the main clutch lever when the human operator operates the main clutch lever into a clutch-in (or clutch-ON) position. Thus, human operator's force necessary to grip and operate the main clutch lever toward the grip portion of the operating handle can be effectively supplemented, so that the main clutch lever can be operated comfortably.
However, when the main clutch lever is to be pivoted from the upper, OFF position to the lower, ON position, the aforementioned travel clutch lever would present the problem that the main clutch lever is hard to pivot downward because the resilient force of the toggle spring becomes resistance to the pivoting movement of the main clutch lever. Namely, because the resilient force of the toggle spring is added to the resilient force of an ordinary return spring used, the pivoting movement of the main clutch lever is subjected to greater resistance, which would thus lower the operability of the main clutch lever.